Termination for electric power cables



E. C. LEE

TERMINATION FOR ELECTRIC POWER CABLES Filed Feb. 19, 1945 Nov. z, 194s.

Patented Nov. 2, 1948 2,452,580 TERMINATION Foa ELECTRIC POWER CABLES Edwin Charles Lee, London, England, asslgnor to Standard Telephones and Cables Limited, London, England, a British company Application February 19, 1945, Serial No. 578,666 In Great Britain February 25, 1944 Claims.

This invention relates to electric power cables and more'partlcularly to terminations therefor. Our prior British patent specification No. 542,842-, describes and claims the manufacture of a power cable termination by lapping insulating material around a conductor core to form a 'barrier of built-up insulation having a uniform-- 'dlameter, coating the built-up insulation with a lacquer which has the property of causing said .insulation to swell, and then fitting over said built-up insulation a preformed sleeve of sub -stantially the same bore so that said insulation upon swelling will tightly engage said sleeve. Prior to that invention it has been a common method of terminating a cable to use a porcelain insulator, considerably larger in diameter than the cable, and to fill the space between the insulator and the cable with an oil or some liquid compound, leaving a small space to take up the expansion of the liquid...With such a method there was the danger that the oil or liquid compound might liow back in-to the cable, leaving a portion of the cable-end exposed and therefore liable to damageA bytracking; oragain, that if the cable was of the oil filled type and the cable run were at a higher level.than the termination then oil might flow into and dissolve the compound in the porcelain insulator so that during subsequent heating oil might leak out of, or even crack, the porcelain. The above mentioned prior patent specification is one of a number which sought to deal with this problem by making a solid seal between a built-up insulation and a close-fitting preformed sleeve.

The present invention carries this preference for a solid seal yet further; whereas the above mentioned patent specification contemplates that the space between the hollow porcelain insulator and the preformed sleeve shall be filled with oil or other insulating compound, the present invention proposes that this space too should be sealed solid. Thus oil or liquid compound is wholly eliminated from the termination.

The following description relates to the accompanying drawing which shows by means of an axial section the manufacture of a power cable termination constructed in accordance with the present invention.

The end of a cable that is to be terminated in the manner of the present invention rst has its lead sheath II stripped back from the cable end to expose the required lengt-h of the insulated coveringr I2 such as a multi-layer winding of impregnated paper tape. Then this insulation I2 is in turn removed for a short distance from the end to expose the conductor core I3, and a copper end ferrule I4 is soldered to the end of the conductor I3. A mounting plate- I5 and a flared sleeve iB xed in the central aperture of the mounting plate are fitted over the end of the cable and positioned a short way down on the lead sheath II. The flared sleeve I6, extending rearwardly, is secured to the sheath II by solder Il. The 'surfaces of core I3, insulation I2, and the short length of cable Il, down to the mounting plate I5. are then lapped with insulating tape to form a built-up insulation I8 of uniform diameter along its length; this tape is preferably of partially acetylated cotton impregnated with a rubber-polystyrene mixture.

With the cable-end thus exposed and built-up, it is ready tore'ceive a tube I9 preformed of in-y sulating material suchas paper impregnated with polystyrene. This tube'has a bore substantially equal to the diameter of the built-up insulation so that it will be a tight fit; it may be fitted endwise or it may be split longitudinally for clamping round. In any ca se the filling is preceded by the step of coating the outside of the built-up insulation, with a solvent for the insulation, such as a lacquerz'then when the .tube I9 is fitted immediately afterwards, the built-up insulation material will tend to swell and give a good tight seal without voids. At'its rearward or bottom end the preformed .tube I9 is received within a copper gland 20 which is fixed in the mounting plate I5. An effective seal between the copper gland 20 and tube I9 is provided in the manner disclosed in our prior British patent specification No. 548,875, namely, by forming peripheral grooves in that part of the tube I9 to be within the gland 20, fitting rubber rings 2i in the grooves so as substantially to fill them, and then after assembly spinning corresponding indentations in the gland to put the rings under pressure. At the forward end is provided a somewhat similar gland '22 overlying and compressing sealing rings 23.

The assembly is now ready to receive the porcelain insulator 24 which is the outermost element; and, as already indicated, itA is one of the features of the invention that there should be a solid seal between the preformed tube I9 and the porcelain 24. This solid bonding may be accomplished by coating the outer surface of the tube I9 with a solvent for the insulating material of the tube, just as in the case of bonding the built-up insulation I8 to the preformed tube I9. Thus, where the tube I9 is impregnated with polystyrene as above mentioned, the coating may be monomeric styrene or perhaps preferably a 3 solution f polystyrene The insul tor 34 is a tight t over the tube IB; and the monomeric styrene poiymerises with time and forms a bonding which prevents the occurrence of voids between the two members. An annular rubber washer 25 its into a. recess in the rear end of the insulator 24 and seals the space between the insulator 24 and the mounting plate i5, while a sleeve 26 fixed in the mounting plate I is spun over a shoulder on the bottom of the insulator 24. At the forward or top end there is an end-cap 21 spun over a shoulder on the insulator 24, and engaging an annular rubber in monomeric styrene.v

washer 2B similar to the washer 25. A nut 22 screwed onto the ferrule I4 clamps the assembly axially. A copper stalk 30 is screwed onto the ferrule I4 above the nut 29. Between the gland 22 and the ferrule I4 is a, copper asbestos Washer 3i.

One of the advantages or the invention is that it enables the size of such terminations to be reduced.

Another and considerable advantage is that it enables most of the assembly to be done in the factory instead of on the site. Because it does not involve the use of a liquid, a sub-assembly consisting of the porcelain insulator 24, preformed tube I9, elements 21, 28, 23, 22, 20, 2|, 25, 2B, and mounting plates I5, I6, can be made up in the factory, leaving for the eld only the job of stripping and building up the cable-end with tape I8 and ferrule I4, fitting the sub-assembly and wiping the joint I1.

It will be noticed that the bore of the porcelain insulator 24, like the outside of the styrenated tube I9 over which it fits, is of plain cylindrical contour, instead of being of the more usual slightly conical shape. The advantage of this is that should any axial. shift occur between the two members, there will be no creation of a gap between them.

What is claimed is:

1. A terminating assembly for an electric cable havingr a conductor, covered by insulation and a metal sheath partly cut back and lapped With tape to form a built-up insulation of uniform diameter along its length comprising, a tubular member of insulating material adapted to tightly engage said insulating tape, a porcelain insulating member tightly fitted over saidv tubular member to form a bonding seal substantially throughout its contact surface, means for sealing said members'at one end to said metal sheath, and

means for sealing the other end of said members to said cable conductor.

` 2. A terminating assembly for an electric cable having a conductor within a metal sheath, said conductor being partly covered and partly uncovered by insulation within the sheath comprisins, an annular vmounting platel adapted to fit over and connect to the metal sheath of the cable. built-up insulation of substantially uniform diameter on the insulation covered portion oi the conductor; an insulating tube adapted to tightly engage said built-up insulation about said cable, an enclosing -porcelain insulator bonded to said tube, means for sealing one end of said porcelain insulator to said mounting plate, and terminating means for connection to the cable conductor and adapted to seal the other end of said porcelain insulator.

3. An assembly in accordance with claim 2, wherein said tube further comprises a preformed sleeve impregnated with polymerized insulating material and bonded to said porcelain insulator by said polymerized insulating material'.

4. An assembly in accordance with claim 2, wherein said mounting plate further comprises,

y a flared sleeve to facilitate wiping a joint to said cable sheath, and said means for sealing said plate to said insulator further comprises a rubber Washer therebetween which is partly recessed into REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,282.003 Scott et al May 5, 1942 2,303,283 Kirkwood et al Nov. 24, 1942 2,362,963 Lee Nov. 14, 1944 FOREIGN PATENTS Number Country Date 542,842 Great Britain Jan. 29, 1942 

